For example, in a cell operation such as rotation and positioning of an ovum in microfertilization or microinsemination, controlling of position and attitude of a cell, being a small sample, is important. As an operation method for a small sample, a method using a manipulator, a method using an alternating electric field, a method using laser light, and a method using vibration are known. Outlines of these methods will be described in the following.
(Method Using a Manipulator)
As a method using a manipulator, for example, a holding pipette is physically hooked and turned, or inner pressure of a holding pipette is varied to suck in or expel, to incidentally vary the attitude of a sample. However, this type of method requires skill and takes a lot of time for a beginner, and is known to be inefficient. With this method, therefore, there is the disadvantage that a system for assisting adjustment of physical attitude and position, or alternatively a system for automatic injection, are required.
(Method Using an Alternating Electric Field)
As a method using an alternating electrical field, attitude and position of a dielectric such as a cell are controlled by, for example, placing a plurality of electrodes inside a dish, and applying an alternating electrical field. With this method, it is necessary to take into consideration damage inflicted on the cell etc. by application of the electric field. Also, arranging a sample with good accuracy close to a glass pipette is difficult, and it is necessary to bring the glass pipette close to the sample. Therefore, the method using an alternating electric field is currently only used in extremely limited operations.
There have also been reports of a method used with organic sample microscopic operations, where electrodes are attached to a holding pipette and an injection pipette, and an alternating electric field generated between the two glass pipettes to carry out rotation of the sample (refer to patent publication 1, below). However, with this procedure there is a problem that a new operation is required to attach electrodes to the glass pipettes.
(Method Using Laser Light)
As a method using laser light, laser light is condensed by a lens, and a transparent sample is manipulated. With this method, by increasing output of the laser light used, it is also possible to perform processing of a few μm or less. This method can carry out non-contact sample manipulation and processing at the same time, but since laser light is used it is not possible to use directly in normal microscopic manipulations, and it is necessary to newly install a dedicated structure. There is therefore the drawback with implementation of this method that is demands extremely high cost.
(Method Using Vibration)
As a method using vibration, a rod-shaped vibrator such as a glass pipette is vibrated, to generate at least one standing wave in the vibrator (refer to patent publication 2 below). With this method, a sample is trapped at a node portion of a standing wave generated in the vibrator, and the sample is rotated.
However, the position of the standing wave node is more or less fixed according to the vibration mode. For this reason, with this method the position where it is possible to manipulate a sample is limited by the vibration mode. In particular, with this method manipulation of a sample at the tip end of a pipette is considered difficult. This is because it considered that a node is not generated at the pipette tip.
Besides the methods described above, there have also been reports of using ultrasound and using thermosetting resin in manipulation methods for microscopic samples, but in practical terms there are still many unresolved problems.
Patent Publication 1
Japanese Patent Laid-open No. 2001-239500
Patent Publication 2
International Patent Publication No. WO01/072951